This application claims the priority of German Patent Application Serial No. 299 19 877.4, filed Nov. 11, 1999, the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to an electromotive adjustment assembly.
Conventional electromotive adjustment assemblies of a type involved here have two rotatable spindles, whereby each spindle is coupled to a gear motor so that the spindles can be driven independently from one another. Such adjustment assemblies are used, for example, to adjust the head part or foot part of a slatted frame. The spindles are aligned, and each spindle carries an elongate spindle nut, which is secured against executing a rotation movement. Each spindle nut is connected to a lever, which is mounted, for example, in fixed rotative engagement to an axle or shaft of a furniture item being adjusted so as to convert a linear movement into a rotating movement of the structure being adjusted.
So-called single drives are also known which include a spindle that carries a spindle nut. Other drives are known that have a rotating spindle and a gear motor which travels along the spindle as the spindle rotates. In general, the rotation speed of spindles in conventional adjustment assemblies is relatively low because the drive is implemented by a worm drive positioned between the motor unit and the threaded spindle. There is, however an increasing need in some cases, to significantly increase, e.g. to double, the pace of the linearly movable output member and, optionally, to significantly increase the adjustment path, without essentially enlarging the overall size of the adjustment assembly.
It is thus an object of the present invention to provide an improved electromotive adjustment assembly, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved electromotive adjustment assembly which allows an adjustment of an attached structure at significantly higher speeds, and establishment of a greater adjustment path than previously known, without substantially enlarging the size of the adjustment assembly.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing at least two spindles disposed in parallel spaced-apart relationship, and a single motor unit coupled in driving relationship with the spindles for rotating the spindles.
Unlike conventional adjustment assemblies, an adjustment assembly according to the present invention uses a single motor unit so that both spindles can only be operated simultaneously. Depending on the configuration, the linear speed of the output member of the adjustment assembly can be significantly increased because the velocities of the components moved by the spindles add up. Moreover, it is also possible by suitably configuring the adjustment assembly to enlarge the adjustment path.
There are many applications for an adjustment assembly according to the present invention. For example, it is possible to install the adjustment assembly according to the present invention in a column to lift, e.g., the table top of a work table. Moreover, it can be integrated in a tubular table leg of a table.
In accordance with a simple embodiment of the present invention, the spindles can be driven by a same number of drive wheels which are in mesh with a gear member driven by the motor unit. The drive wheels are then the driving component of the drive for the spindles. As the rotation speed of the spindles should also be relatively low in an adjustment assembly according to the present invention, the gear member and the drive wheels define a gear mechanism in the form of a reduction gear unit. An especially high speed ratio between the output member (output journal) of the motor unit, e.g. an electric motor, and the spindles can be realized when the drive wheels for the spindles are identical worm wheels which extend at an angular offset of 180xc2x0, and when the gear member being rotated by the motor unit is a worm wheel. Both spindles are then driven in opposite directions, whereby their speeds are the same when the worm wheels are identical.
According to another feature of the present invention, the worm wheels may suitably be provided with semi-globoid toothed surface.
The adjustment path and the velocity of the structure being attached to the output member of the adjustment assembly can be significantly increased, compared to conventional adjustment assemblies, when one worm wheel has an internally threaded bore to form a movement-permitting thread, for engagement with a first one of the spindles, and the other worm wheel is connected in fixed rotative engagement on the other second spindle. As a consequence, there are several options for implementing the adjustment. According to one variation, the first threaded spindle can be non-rotatable so that the attached worm wheel travels along the threaded spindle. When using the adjustment assembly for a liftable column or for a table leg, the tabletop to be vertically adjustable could then be connected via a coupling element with the second threaded spindle. Provision should then be made that the gear motor comprised of the worm and both worm wheels as well as the motor unit is guided in a guide of the column or the table leg. According to another variation, the gear mechanism in the form of worm wheels and worm is stationary so that the first threaded spindle can travel in linear direction relative to the associated worm wheel. In order to increase the adjustment speed and the adjustment path, the enclosing tube of the adjustment assembly should then be of telescoping configuration.
In an adjustment assembly according to the present invention, the second spindle in fixed rotative engagement with driving worm wheel is normally connected with the structure being adjusted, for example a tabletop, via additional components. Therefore, it is proposed to mount onto the second spindle a spindle nut which is secured against executing a rotation movement so as to travel only in a linear direction. Suitably, the spindle nut is connected to a lifting or thrust tube which thus moves in and out in accordance with the travel of the spindle nut. The lifting or thrust tube is surrounded by a flanged tube which accommodates also a holed rail for attachment of limit switches by which the travel of the spindle nut is limited between predetermined end positions. The positions of the limit switches may be modified to the situation at hand so that applications in which the entire travel path of the spindle nut cannot or should not be exploited can also be satisfied. In the case at hand, the limit switches are determinative for the lift of the entire drive.
According to another feature of the present invention, the spindles are supported at their end zones that are associated to the worm wheels by bearings, suitable rolling-contact bearings. In order to keep the distance between the spindles to minimum to realize a compact construction, it is proposed to provide the bearings for support of each spindle with different diameters, whereby diagonally opposite bearings have a same diameter.
Suitably, the worm wheels in engagement with the driving worm are disposed offset to another at an angle of 180xc2x0.
According to another feature of the present invention, the drive wheels are defined by center planes disposed perpendicular to a rotation axis of the worm, with the center planes of the drive wheels extending offset to one another and at a distance to the rotation axis of the worm to thereby provide access to fastening elements. Hereby, the offset of each worm wheel with respect to the rotation axis of the worm is the same. This offset can be realized in a simple manner by providing the circumferential toothed surface of the worm wheels of semi-globoid configuration.
The spindles may or may not have a same pitch. It is also possible to so configure an electromotive adjustment assembly according to the present invention as to be self-locking. In situations in which the structure being adjusted is exposed to extremely great forces, there is, of course, the option to equip an electromotive adjustment assembly according to the present invention with a holding brake, for example in the form of at least one wrap spring. Certainly, if an electromotive adjustment assembly according to the present invention is not self-locking, the provision of a suitable brake is required in any event.
As an alternative to the use of limit switches for defining the end positions of the linearly moving components, for example the spindle nut or the lifting or thrust tube, it is also possible to define each end position by an mechanical blocking device, preferably in the form of a stationary or adjustable stop member which interacts with an electrical measuring. The measuring device registers an increase of a current strength in the motor unit when a linearly moving component strikes against the stop member, and forms a commensurate signal for cutting the motor unit. Another possibility is the provision of an electric and/or optic recognition device to define the end positions. An example of such a device includes proximity switches or the like. Conceivable are also position-determination devices for defining the end positions, which are so configured that the motor unit is cut when the linearly moving components occupy a predetermined position. Another variation includes the determination and optional storage of revolutions of rotating components so that a signal can be formed by an evaluation unit for cutting the motor unit when the linearly moving component occupies a predetermined position, based on the correlation between number of revolutions and advanced travel path. Rotating components in adjustment assemblies involved here is the rotor of the motor unit or the spindle. It is also feasible to register the revolutions of the gear members of the reduction gear unit, or the revolutions of those gear members that are disposed in the power train ahead of the reduction gear unit. Finally, it is also possible to measure the path covered by the linearly moving components.
An electromotive adjustment assembly according to the present invention has the advantage that the torque being transmitted is distributed onto the spindles, so that the service life of the spindles can be enhanced and the overall size can be reduced, and the use of qualitatively inferior materials may be used.